Permafrost Regions Roadbed Calculation Principle And The Critical Height Of Research

Taking the Qinghai-Tibet highway for example, the author of this paper presents a finite element method in which all the boundary conditions such as radiation, convection, wind speed, evaporation, etc. are considered, meanwhile, this paper gives formulas to simulate every field factor. For the temperature of the natural surface of Tuotuo River area and the surface of the test embankment, the results calculated by this paper method agree well with actual field measurements. Furthermore, the paper presents the calculation formulas for the heat-conducting coefficient and heat specific volume of sub-clay and grit soil, obtains a calculation formula for the earth surface evaporation according to the water surface evaporation, offers a way to determine the transverse wind speed along the embankment surface. And also through the analysis and induction of the solar radiation on the slopes of both road sides, the author recommends a calculation formula for the slope coefficient and the values of the slope coefficient for the subgrade with different dip angle and strike. Based on this the transverse distribution of all eternal factors along the embankment surface can be calculated. On the basis of the previous results, the paper discusses the transverse temperature difference and the yearly changing laws of temperature field in frozen embankment, analyses the transverse temperature difference and the changing process of temperature field with the passing of time after the embankment is built, obtains the yearly limit needed for yearly steadily changing and greater changing of temperature field in embankments with different heights, finds the existence of soilmelting cores in the embankment and their changing laws, and points out that the asymmetric characteristics of temperature distribution in the surface soil is strong in winter and weak in summer. The author also discovers that the temperature changes in the deep soil occur 5 months later than those in the surface soil as well as atmospheric temperature.By simulating the complicated boundary conditions, a two-dimensional moisture migration calculation model is suggested in this paper, it can be used to analyze the heterogeneous embankment. It is proposed that the hydraulic head should be made up of gravitational head, martin suction head, temperature head and phase change head. The concept and calculation method of temptation head and phase change head is suggested. Furthermore, the calculating process and the method to determine theparameter of the model are introduced, and then the form mechanism and calculation o f the frozen fringe and thaw fringe is discussed. Based on the research of moisture migration and temperature field, the calculation for moisture-temperature is achieved in frozen soil subgrade. According to above results, the paper realizes the calculation of the coupled temperature and moisture migration.This paper establishes a two-dimension model for the stress and deformation of frozen soil subgrade, which can completely consider the great change in soil property caused by water and temperature conditions, the significant creep behavior, the temperature-caused self-volume deformation and the transient deformation resulted from applied loads. Meanwhile, the author gives the FEM calculation process and partial parameter values, and introduces the method to decide the frozen soil strength.It broadens the critical height concept as the height to ensure the embankment safe. Through the analysis on the temperature distribution and the deformation pattern in the frozen soil subgrade, the paper not only presents that the upper value and lower value exist in the critical height of frozen soil subgrade, but also gives the method to calculate the upper and lower critical height for sand-grade pavement and asphalt pavement.